The principal of electrostatic attraction has been used for many years to enhance the removal of contaminants from air streams. There are three primary categories of air electrostatic cleaners: electrostatic precipitators, passive electrostatic filters and active field polarized media air cleaners, which are sometimes known under different terms.
Electrostatic precipitators charge particles and then capture them on oppositely charged and/or grounded collection plates.
A passive electrostatic filter (also know as an electret) employs a media (or combination of different media) that through some combination of treatment and/or inherent properties has an electrostatic charge. Particles entering the filter media that have an electrostatic charge are attracted to the charged media filter materials that have the opposite electrostatic charge.
In a polarized media air cleaner described for example in U.S. Pat. No. 7,708,813 and 2012/0260803, both of which are incorporated by reference as if fully set forth herein, a voltage differential between elements is used to create an electrostatic field that polarizes the fibers of a media pad and the surface charge of airborne contaminants. This significantly enhances capture and loading of the contaminants. In these systems, there is a high voltage connection between a high-voltage power supply and a probe centrally-located conductive screen of a media pad positioned between grounded exterior screens. The connection is critical to the function of the overall system as the voltage differential between the center screen and the ground screen(s) creates the electrostatic field. This connection point, however, can be a weak point in the system and may fail, rendering the polarizing feature in the air cleaner ineffective.
The reason that this can be a failure point is because the filter material itself is often a sparse material. Because air must pass through the system with as little resistance as possible, screens and other materials in a filter may be made from sparse material. This does not make for a solid electrical connection. Further, some of the byproducts of an incomplete connection are arcing, ionization, and ozone production. All of these will tend to breakdown a variety of materials and further exacerbate the problem. Therefore, if the center screen is a relatively sparse material and the high-voltage probe is relatively small, it may be difficult to assure a reliable connection between the two.
Thus, any object connected to the material including a conductive probe becomes a stress point in a sparse and minimally tough material.